1. Field of the Invention
The present invention relates to a linear guide apparatus used in a machine tool, a conveyer device, and the like. More specifically, the present invention relates to a linear guide apparatus which can be applied when guide rails are not only straight rails, but also curved rails, or combinations thereof.
2. Related Background Art
A linear guide apparatus generally comprises guide rails which extend in the axial direction and a slider which engages with the guide rails and can move relatively thereto, wherein a pair of upper and lower ball rolling grooves parallel with each other are formed on each side surface of the guide rails. On the other hand, loaded ball rolling grooves corresponding to respective ball rolling grooves of the guide rails are formed on both inner surfaces of the slider. Further, ball circulation paths to be communicated with respective loaded ball rolling grooves are formed inside the slider. A multitude of balls endlessly circulate through the ball circulation paths and the loaded ball rolling grooves. As the balls roll in the loaded ball rolling grooves, they carry the load so that the slider can smoothly shift along the guide rails.
In the linear guide apparatus having the above-mentioned constitution, the slider is guided, in most cases, by straight guide rails so as to shift straight. But in some cases, an object which is fixed to a table has to be guided and carried not only along a straight path but also along a curved path or combinations thereof. A bearing apparatus for both linear and curved rails which can be used in all the has been disclosed in U.S. Pat. No. 4,844,624.
In this conventional apparatus, straight load carrying region(s) and curved load carrying region(s) of predetermined curvature are provided together in the same loaded ball rolling groove (load carrying surface) which is part of an endless track in a slider (bearing). When ball rolling grooves (track surfaces) of the guide rails (railways) are straight, the balls rolling in the straight load carrying regions carry the load. On the other hand, when the ball rolling grooves are curved, the balls rolling in the curved load carrying regions carry the load.
In the above-mentioned conventional apparatus, however, as the straight load carrying region(s) and the curved load carrying region(s) with predetermined curvature are alternately provided in the same loaded ball rolling groove, the following problem will happen when the slider moves along the curved portions of the guide rail.
That is, as schematically shown in FIG. 8, the load is given to the balls in the curved load carrying regions B, D and F of the loaded ball rolling grooves of the slider 2, while the balls in the straight load carrying regions A, C and E are not restricted by the ball rolling grooves of the guide rail 1 and shift rolling freely along the endless circulation paths. As a result, the balls rolling in the straight load carrying regions A, C and E rattle to make a big noise. Similarly, when the slider 2 moves along the straight portions of the guide rail 1, the balls in the curved load carrying regions B, D and F shift rolling freely and rattle to make a noise.